The present invention relates to a fuel control for an internal combustion engine designed to operate with a fuel other than gasoline, and more particularly to a fuel pressure control for such an engine.
In general, an alternate-fuel engine is a spark-ignition internal combustion engine designed to operate with a fuel other than gasoline, and encompasses both single fuel engines and so-called dual-fuel engines. Regardless of the type of fuel, the overall objective of the fuel control is to maintain a desired air/fuel ratio for purposes of meeting fuel economy and emission control targets. However, the fuel control strategies vary to some degree depending on the type of fuel being utilized. For example, precise fuel pressure control is much more important with alternate fuels such as compressed natural gas (CNG) or liquid propane (LP) than with gasoline. Accordingly, most alternate-fuel engines utilize closed-loop fuel pressure control, with one or more sensors for precisely measuring the fuel pressure and a pressure adjustment mechanism for maintaining the measured fuel pressure at a fixed or predetermined value. The fuel pressure adjustment mechanism may be either an adjustable fuel pressure regulator or an adjustable speed fuel pump. However, it is difficult to schedule the desired fuel pressure for optimal air/fuel ratio control, and the required fuel pressure sensors significantly increase the fuel system cost. Accordingly, what is needed is an improved fuel pressure control that provides optimal air/fuel ratio control, and that does not require precise fuel pressure measurement.
The present invention is directed to an improved fuel pressure control for an alternate-fuel engine, wherein adaptively learned corrections for fuel injection pulsewidth based on air/fuel ratio sensing are also utilized to dynamically adjust a base fuel pressure control signal. The fuel pressure control may therefore be characterized as an open-loop control with a closed-loop correction term based on air/fuel ratio error. The control dynamically adjusts the fuel pressure in a manner to optimize the air/fuel ratio control instead of controlling to a predetermined pressure, and fuel pressure measurement is not required.